Compression-type seal.



W. T. BIRDSALL. COMPRESSION TYPE SEAL. APPLICATION FILED MAY 4. 1915.

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WITNESSES AT'TORNEY UNITED STATES PATENT OFFICE.

WILFRED '1. IBIRDSALL, 0F MONTGLAIR, NEW JERSEY, ASSIGNOR, BY MESNEASSIGN- MENTS, T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, ACORPORA- TION OF PENNSYLVANIA.

COMPRESSION-TYPE Specification of Letters Patent.

Patented May 30, 1916.

Application filed May 1915. Serial No. 25,865.

to provide a device of the character described that will be simple,inexpensive and rugged in construction.

Referring to the accompanying drawing, Figure 1 is a side view,partially in section and partially in elevation, of a seal embodying myinvention; and Figs. 2 and 3 are plots illustrating and indicating therelation of the different coefficients of expan sion in my seal.Hitherto, when it has been desired to introduce electric current intoevacuated containers of vitreous material, it has been necessary to fusethe conductor to the wall and the material which-has been used with mostsuccess as a sealing-in conductor has been platinum. When it is desiredto employ platinum, however, inlarge amounts, as is 36 necessary forlarge-capacity rectifiers, its

cost'becomes prohibitive.

I have found, by surrounding a leadingin wire of any material, such, forexample, as iron or tungsten by a mass of elastic material such, forexample, as glass, and by surrounding said glass by a band of materialhaving high tensile strength, said band of material being shrunk on sothat the mass of glass is at all times maintained under compression, Iam enabled to provide, in difl'erent annular zones of the glass,apparent coefficients of expansion which vary uniformly from that of thewire to that of the surrounding band. By choosing, therefore, a.compressing band the coefiicient of expansion of which, with respect. tothe coefficient of the wire, lies beyond the coefiicient of .thematerial in the container, I i am enabled to provide a zone of glasshaving an apparent coefficient which is substantially that of thecontainer and, by fusing the container wall to said zonein any wellknown manner, I am enabled. to obtain a vacuum-tight joint between thecontainer Wall and the leading-in wire, in spite of great divergenciesin the coeificients of expansion therebetween.

Referring to the accompanying drawings -for a more detailedunderstandingof my invention, I have shown a leading-1n wire at 4 inFig. 1. The leading-in wire 4 is surrounded by, and supports, a mass ofelastic material 5 formed, preferably, of glass. A band of material 6surrounds the body of glass 5 and is formed of material having hightensile strength, such, for ex ample, as steel or brass. The band 6 isshrunk upon the body of glass .5 and is of such tensile strength that itwill maintain the body in a state of compression throughout a wide rangeof temperature variation.- Under these conditions, the body 5 will notfollow the ordinary law under which all of its component portions wouldexhibit the same coefficient "of linear expansion, butv the zone lyingadjacent to the wire 4 will be forced to assume an apparent coefiicient'of expansion closely approximating to that of the wire 4. In likemanner, the zone of the mass 5 lying adjacent to the band 6 will beforced to assume an apparent coefiicient of expansion closelyapproximating that of the material composing the band 6. All zones lyingbetween the wire 4 and the band 6 will exhibit different apparentcoefficien'tsof expansion, there being a radual transition from thevalue exhibite ad jacent the wire 4 to the value exhibited adjacent theband 6. The neck of the container of. a vapor electric device is shownat 7 and the coefiicient of the band 6 is so chosen with respect to thecoeflicient of the wire 4 that it lies beyond the coeficient of thematerial composing the container 7. For example, if the material of thecontainer 7 has a lower coeflicient than that of the wire 4', thematerial ofthe band 6 will be chosen to have a still lower 'coefiicient,and vice versa. As there is a gradual transition in the body 5 from anapparent coeflicient approximating that of the wire. 4 to thatapproximating the coeflicient of the band 6, 'a certain zone will befound having .an apparent coefilcient of expansion closely this zone,there will be no difierential expansion tending to rupture the seal, anda vacuum-tight connection may be readily provided between the container7 and the wire 4.

In order to compute the necessaryradius for the neck of the container 7to satisfy the above-described conditions, recourse may be had to asimple graphic treatment, as

illustrated in Figs. 2 and 3. Let the distances CD and CF be laid out onan ordinate to correspond, respectivel to the radii A and B of the wire4 and 0 the inner surface of the band 6 at any arbitrary temperature. Inlike manner, let the distances GH and GK represent the respective radiiof said .two members at' a different temperature.

' tainer 7 to the same scale as has been used dinate DF at a pointgeometry that any hne in plotting the coefficients of the members 4 and6. The line MJ will intercept the or- E and the distance OE will be thedesired radius X for the neck of the container 7 to the proper scale. Toprove this, consider a particle in the mass 5 lying at distance X fromthe wires. If the mass 5 is homogeneous, as must be assumed, thisparticle will always divide the distance between the wire-and theoutside band in the same ratio. In Fig. 2 we measure this distance asDF. Then we know by drawn through M will divide similar llnes, such asHK, in the same ratio that it divides DF. If the radius X is CE in Fig.2, it follows that points of intersection with the different ordinatesby the line MJ will give the radii of the particle of glass undercompression at the temperatures respmtivel corresponding on the diagramto each ordmate. But the position of the line MJ is bound to indicatethe raneck of the container 7 at each temperature. It will also indicatethe position of the particle of the mass 5 at all temperatures and thecoefiicient of the zone in the mass 5 at the radius X must be the sameas that of the container 7. It therefore follows that a tube the meanradius of which is determined as above can be sealed directly to thewire 4 without danger of rupture.

If a seal is to be made without the central wire 4, then, in Fig. 2, theline MDH will be omitted and the point M will become the intersection ofthe line FK with the horizontal axle.

dius of the In the specific case when the wire 4 and the band 6 have thesame coefficient, the point Mwill lie at infinity and, since the lineMEJ must pass through this oint, it would be parallel with FK and D ineach case. That is, the coeflicient of the container 7 must-be the sameas that of the wire and of the band.

Referring to the diagram shown in Fig. 3, the conditions are exactly thesame as shown in Fig. 2 except that the coefiicient of the band 6 isless than that of the wire 4 and, accordingly, the computation must bemade on opposite sides ofthe point of intersection. Particularattention, should be paid to the fact that the values of thecoefficients of the wire and of the clamping band should always be sochosen that they lie on opposite sides of the coefficients of thematerial of the container.

While, throughout this case, I have described the band 6 as beingcomposed of metal, it may .very well be composed of glass or of anyother material having suitable properties.

I have described the external band '6 as exerting pressure upon themass5 but, within certainlimits determined by the coherence of thejoints, the member 6 may exert tension on the mass of the member 5,establishing forced coefiicients of expansion in the intermediate zonesthereof in the same manner as under conditions of pressure.

Many materials, such, for example, as compound metals, have an expansionline which is curved or which comprises two relatively straight linesmeeting at an angle.

If the seal is raised to a temperature where the external forces actingupon the intermediate mass 5 are modified, the different zones will obeynew laws, following an expansion line between the lines of the members 4and 6. If either the member 4 or the member 6 entirely other laws, theapparent coeflicient belng raised if the wire 5 first releases and beinglowered if the band 6 is the first to cease operation.

With certain combinations ofmaterials,

a seal having excellent manufacturing characteristics, such, forexample, as cheapness, ease of manipulation, and great mechanicalstrength, may be produced in accordance with my invention but mayexhibit a tendceases to act upon the mass 5, the intermediate zones ofthe latter will follow from the spirit thereof that no limitationscomprising a massof material having a plu-- rality of different forcedcoefficients of expansion in different zones thereof, a seal betweensaid wire and a zone of said mass of corresponding coefficient, and aseal between said tubular member and a zone of said mass ofcorresponding coefficient.

3. In a seal, the combination with two members between which a tightconnection is to be made, of a third member, means for forcing saidthird member into close contact with one of said first named members andfor imposing upon different portions of said third member differentapparent coefiicients of expansion, and means for attaching the other ofsaid first named members to a portion of said third member correspondingto its own coeflicient of expansion.

4. A seal between a tubular member and a wire extending therethrough andhaving a difierent coeflicient of expansion therefrom comprising a massof material surrounding said wire, means for forcing said mass intointimate contact with said wire and for causmg the outer portlon of saidmass to assume difi'erent coeflicients of expansion such that thecoefiicient of the tubular member is between those of the wire and ofthe outer,

portion of said mass, and a seal between said tubular member and anintermediate zone in said mass having a coefficient of expansioncorresponding to its own.

5. The combination with a wire, of a mass of elastic material mountedthereupon, a clamping member surrounding said mass and forcing theportions thereof adjacent said wire to assume a coeflicient of e ansionsimilar to that of the wire while orcing annular zones in said mass oflarger radius from said wire to assume coeflicients of expansiondiffering by continuously increasing amounts from that of the wire, anda tubular member having a coefiicient of expansion differing from thatof the wire and sealed to a zone in said mass having a coefficientcorresponding to its own.

. 6. The combination with a wire, of a mass of glass mounted thereupon,a metallic band shrunk around said mass of glass so that said mass ismaintained in compression throughout a wide temperature range and isforced to assume apparent coefficients of expansion in the portionsadjacent to said wire and to said band of values corresponding,respectively, to those ofthe wire and band and in intermediate zones toassume apparent coefiicients of expansion of intermediate values, and amember composed of material having a coeflicient between those of thewire and of the band and sealed to a portion of said mass having acoeflicient corresponding to its own.

7. The method of joiningtwo members having different -coeiiicients ofexpansion which comprises imposing upon different portions of a thirdmember a lurailty of different apparent coeiiicients 0? expansion, andsealing .each of said first named members to a portion of said thirdmember having a coefiicient corresponding to its own.

8. The method of joining two members having different coefficients ofexpansion which comprises imposing upon difi'erent portions of a thirdmember of elastic material a plurality of different apparentcoeflicients of expansion by continuously applied external force andsealing each of said first named members to a portion of said thirdmember having an apparent coeflicient corresponding to its owncoefficient.

In testimony whereof, I have hereunto subscribed my name this 28th dayof April,

WILFRED T. BIRDSALL. Witness:

ALFRED H. Enem

